1. Field of the Invention
This invention relates to a gas-liquid separation, more specifically gas transmission pipeline drips for removing liquid contaminants from gas streams.
2. Description of the Related Art
Underground natural gas transmission pipelines may be contaminated by liquids during operation. Such liquid contaminants include hydrocarbon condensations, lubrication oils, produced water, and chemicals used in the production, treatment, compression or dehydration of the gas. These contaminants may cause injury to or interfere with the proper operation of the lines, regulators, filters, meters or other appliances.
Gas transmission pipelines use "drips" which are installed in the pipeline at regular intervals to collect the liquid contaminants. These drips must often be designed to allow a device called a "pig" to travel internally along the length of the pipe without obstruction. A cleaning pig is used to mechanically remove contaminants which have collected in areas such as low spots in the pipeline. An inspection pig uses instruments to record features such as geometry, wall thickness and orientation of the pipeline. It is important that the drip not detrimentally effect the gas flow through the pipeline by creating head losses in the proximity of the drip. Yet the drip should also be effective in removing liquid contaminants.
The drawback of using traditional drips is that their efficiency may be adequate for stratified two-phase gas-liquid flow regimes; however, the efficiency decreases at higher gas velocities where the two-phase flow regime changes from stratified to annular flow.
There are known devices for removing from a gas stream, suspended particulate such as liquid droplets. For example U.S. Pat. No. 4,180,391 issued Dec. 25, 1979 to Perry, Jr. et al. discloses a device which uses vortical generators to create a swirling motion in a gas stream. In Perry, the particles are removed from the gas stream with a portion of gas (scavenging gas) through ejection ports of the tube, into a housing chamber. The pressure in the housing chamber is greater than in the conduit, which would inhibit movement of liquid out of the tube at high gas velocities. In Perry, this pressure differential is employed to draw the scavenging gas back into the main stream, further downstream in the conduit. However, the vortical generator employed by perry obstructs the tube. Thus operation of a pig would not be possible in Perry. Furthermore, Perry is designed for use with low gas flow rates, thus requiring vortical generators to force the particulates to the wall of the conduit.
It is an object of this invention to provide a gas pipeline drip which can allow free passage of cleaning and inspection pigs but which effectively separates liquid contaminants at both low and high gas velocities.